In GERAN #62, a study item on “Cellular System Support for Ultra Low Complexity and Low Throughput Internet of Things” was approved. The aim was to study both the possibility of evolving the current GERAN system and the design of a new access system towards low complexity and low throughput radio access technology to address the requirements of cellular internet of things. The objectives of the study were: improved indoor coverage, support for massive number of low throughput devices, low delay sensitivity, ultra-low device cost, low device power consumption and (optimised) network architecture. As per the PCG #34 decisions, it was agreed to move the normative phase of a single “clean-slate solution” to 3GPP Long Term Evolution (LTE). This feature is called NarrowBand Internet of Things (NB-IOT).
3GPP LTE represents the project within the third generation partnership project, with an aim to improve the UMTS standard. 3GPP LTE radio interface offers high peak data rates, low delays and increase in spectral efficiencies. The LTE ecosystem supports both Frequency division duplex (FDD) and Time division duplex (TDD). This enables the operators to exploit both the paired and unpaired spectrum since LTE has flexibility in bandwidth as it supports 6 bandwidths: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz.
The objective of this new study on NB-IOT is to specify a radio access for cellular internet of things, based to a great extent on a non-backward-compatible variant of the Enhanced Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (E-UTRA). This variant addresses improved indoor coverage, support for massive number of low throughput devices, low delay sensitivity, ultra-low device cost, low device power consumption and (optimised) network architecture.
NB-IoT should support 3 different modes of operation:
1. ‘Stand-alone operation’ utilizing for example the spectrum currently being used by GERAN systems as a replacement of one or more Global System for Mobile Communications (GSM) carriers.
2. ‘Guard band operation’ utilizing the unused resource blocks within an LTE carrier's guard-band
3. ‘In-band operation’ utilizing resource blocks within a normal LTE carrier
When NB-IoT is deployed as part of an existing LTE system (like in options 2 and 3), transmit power needs to be boosted in radio resources used for the NB-IoT (e.g. physical channel such as resource block) to meet the requirement of high coverage, i.e. power allocated to NB-IoT radio resource (e.g. resource block) is in general greater than the power allocated to an LTE radio resource (e.g. LTE resource block, resource element, etc). This in turn reduces the coverage of the LTE system, thereby reducing the data throughput.